So-called SEPIC converters have the advantage over other converter designs, for example in comparison to step-up converters, that the output voltage of the converter can be set as desired within a relatively wide range and, in particular, may also be less than the voltage amplitude of an AC supply voltage. The circuit design for the SEPIC converter is familiar to those skilled in the art and therefore need not be described in detail here. However, reference will be made in supplementary fashion to the different explanations in the further course of this description.
A storage capacitor, which supplies the downstream circuit elements with a DC voltage, can be charged by a SEPIC converter. In this case, the SEPIC converter generally has the function of a power factor correction circuit which is used to prevent the capacitor from only being charged from the AC voltage when the instantaneous voltage value of the AC voltage is higher than the voltage applied to the capacitor. This prevents the short-term, pulse-like charge currents in the vicinity of the voltage maxima of the AC supply voltage which result on a regular basis in an impermissibly strong harmonic spectrum.
It is also known in the case of SEPIC converters to carry out so-called ripple current compensation. For this purpose, the two inductances of the converter are coupled and specific conditions are maintained when tuning the inductances. This design makes it possible for a high DC component and a very low radiofrequency component to flow through one of the two inductances.